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Posted to issues@solr.apache.org by "Bruno Roustant (Jira)" <ji...@apache.org> on 2022/12/16 10:43:00 UTC

[jira] [Resolved] (SOLR-16438) Shard split should be able to set preferred leaders on other replicas

     [ https://issues.apache.org/jira/browse/SOLR-16438?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ]

Bruno Roustant resolved SOLR-16438.
-----------------------------------
    Fix Version/s: 9.2
       Resolution: Fixed

Thanks [~dsmiley] for the review!

> Shard split should be able to set preferred leaders on other replicas
> ---------------------------------------------------------------------
>
>                 Key: SOLR-16438
>                 URL: https://issues.apache.org/jira/browse/SOLR-16438
>             Project: Solr
>          Issue Type: Improvement
>      Security Level: Public(Default Security Level. Issues are Public) 
>            Reporter: Bruno Roustant
>            Assignee: Bruno Roustant
>            Priority: Major
>             Fix For: 9.2
>
>          Time Spent: 1h 10m
>  Remaining Estimate: 0h
>
> Currently, shard split always create a first replica for each sub-shard on the current host. Then it creates other replicas and their corresponding sub-shards are in RECOVERY state. The effect is that the first replica (on the current host) is always the leader, meaning that if the sub-shards are split themselves, their sub-sub-shards leaders are also on the same host.
> This can lead to very unbalanced situation where the same host is the leader for a whole set of shards.
> A solution to distribute evenly the leaders is to flag some other replicas with the preferredLeader property during the split. Then a rebalance-leaders command can elect the appropriate leaders. If we do that for each split, then all the sub-shards have their leaders correctly balanced.
> To go further, we can improve CollectionsHandler#CollectionOperation to support combined operations. That way a CollectionOperation#SPLITSHARD_OP can trigger a split op, then a wait for split completion op, and then a rebalance leaders op.



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